By Ashley Dean and Erin Hodgson
2025 was the sixth year of a coordinated effort to monitor corn rootworm adults across Iowa and the fifth year of combining this effort with the Regional Corn Rootworm Monitoring Network. The Hodgson Lab received funding from the Agricultural Stewardship Technical Committee to distribute traps to volunteer cooperators across corn-growing regions in the U.S. and Canada. The 2025 regional report is published, but this article summarizes the Iowa results in greater detail.
Trap site information
In 2025, data were reported to the regional network for 170 corn rootworm trapping sites. The Hodgson Lab coordinated 40 sites, and the Iowa Soybean Association contributed data for another 130 sites. All sites were corn in 2025; 69 sites were corn the previous year (continuous corn production), while 100 sites were previously soybean (corn-soybean rotation).
Issues with corn rootworm prior to 2025 were reported for very few sites, but goosenecking/lodging and high beetle populations were reported for 15 sites. Suspected resistance to Bt was only reported at one site, and suspicion of resistance to crop rotation was not reported.
Despite the unknown history of corn rootworm issues in these fields, at least one management tactic was used specifically for corn rootworm at 100 sites, including 41 sites that were soybeans the previous year. Multiple management tactics for corn rootworm were used at half of those sites, with Bt hybrids + foliar insecticides being the most common (18 sites, seven of which were rotated), followed by Bt hybrids + soil-applied insecticides (15 sites) and Bt hybrids + soil-applied insecticides + foliar insecticides (11 sites).
Entomologists do not recommend using multiple tactics to manage corn rootworm, as research demonstrates that multiple management tactics could hasten resistance development (McColluch and Gassmann 2024), especially when Bt resistance is prevalent in the landscape. Crop rotation is still the most effective management tactic for corn rootworm, and using a single, effective tactic in continuous corn is more cost-effective.
Beetle counts
Corn rootworm adults are mobile, and populations vary across the landscape. It is difficult to know where beetles caught on traps originate, but research demonstrates that significant feeding injury can be expected the following year when at least two beetles/trap/day are captured on yellow sticky cards. This threshold determines whether alternative management should occur the following growing season. In 2025, only 6.5% of sites in Iowa reached the trapping threshold (Figure 2): eight of these sites were in continuous corn, while three were rotated. 11.6% of continuous corn sites reached threshold, while 3.0% of rotated sites did.
Source : iastate.edu